Thread: raid pci card
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Old 30th April, 2005, 09:54 AM
Aedan Aedan is offline
Chief Systems Administrator
Join Date: September 2001
Location: Europe
Posts: 13,075

Hardware RAID 5 is typically slightly slower than software RAID 5. Why? Well, the usual hardware used on a RAID 5 card is a 100MHz processor. Compare that to the main CPU which is sitting there with GHz worth of speed, and you can quickly see why.

Additionally, most hardware RAID 5 cards have cache memory onboard (If it doesn't, it's probably not doing anything much in hardware). Whilst this sounds good in theory, you have to realise it's on the wrong side of the PCI bus to have much of an impact. Data that is cached on the RAID 5 card has to go across the 133Mbyte/sec PCI bus. Data that is cached in main memory only has to go across a 1+Gbyte/sec memory bus.

On the other hand, RAID 5 hardware tends to be a bit more reliable, as the RAID 5 control is seperated from the main system. One thing to bear in mind is that typically RAID 5 doesn't offer great performance. RAID0 and RAID1 offer far higher performance levels than RAID 5 does.
Any views, thoughts and opinions are entirely my own. They don't necessarily represent those of my employer (BlackBerry).
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